Electronic circuits using coupled multi-inductors

ABSTRACT

Coupled multi-inductors and their applications. An apparatus includes several circuit stages. Each circuit stage includes an inductive element that overlaps with the inductive elements of its adjacent circuit stages, forming a loop of coupled circuit stages. The apparatus may be, for example, a multi-phase oscillator with multiple oscillators that are magnetically coupled to each other for generating oscillation signals at different phases. The apparatus may also be, for example, a phase interpolator for combining input signals.

BACKGROUND

The present disclosure relates to coupled multi-inductors and theirapplications.

Multiphase clocking schemes are ubiquitous in radio frequency and highspeed systems. In systems that use multi-phase clocking, multiple clocksignals are generated such that each clock signal has a predictablerelative phase offset from the other clock signals. Multiple clocksignals with certain phase relations can be generated by multipleoscillators. One type of multi-phase clocking is quadrature clocking inwhich the clock signals are ninety degrees out-of-phase with each other.Improving the frequency and phase accuracy as well as the stability ofsuch signals can be important for increasing system performance andefficiency

BRIEF DESCRIPTION OF THE DRAWINGS

The teachings of the embodiments herein can be readily understood byconsidering the following detailed description in conjunction with theaccompanying drawings.

FIG. 1A illustrates a single stage of a magnetically-coupled oscillatorin a loop of magnetically-coupled oscillators according to anembodiment.

FIG. 1B illustrates a phase diagram of currents/magnetic flux at one ofthe output nodes of the oscillator of FIG. 1A, according to anembodiment.

FIG. 2 is a circuit diagram further illustrating the oscillator of FIG.1, according to an embodiment.

FIG. 3 illustrates magnetic coupling between several oscillators,according to an embodiment.

FIG. 4 illustrates a multi-phase oscillator with fourmagnetically-coupled oscillators, according to an embodiment.

FIG. 5 illustrates the phase relationship of the output oscillationsignals from the multiphase oscillator of FIG. 4, according to anembodiment.

FIGS. 6A, 6B, 6C, 6D and 6E illustrates a structure ofmagnetically-coupled inductors for the oscillators of FIG. 4, accordingto an embodiment.

FIG. 7 illustrates a structure of magnetically-coupled inductors for amulti-phase oscillator having three oscillators, according to anotherembodiment.

FIG. 8 illustrates a phase interpolator/mixer that uses themagnetically-coupled inductors of FIG. 6A, according to an embodiment.

FIG. 9 illustrates a block diagram of coupled circuit stages, accordingto an embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS

Embodiments of the present disclosure relate to coupled multi-inductorsand their applications. In one embodiment, an apparatus includes severalcircuit stages. Each circuit stage includes an inductive element thatoverlaps with the inductive elements of its adjacent circuit stages,forming a loop of coupled circuit stages. The overlaps between theinductive elements enable energy to be transferred between the circuitstages via inductive coupling. Most pairs of the inductive elements mayinduce the same energy in each other, except for one pair of inductiveelements that is inverted from the rest of the pairs in the loop. In oneparticular embodiment, the apparatus is a multi-phase oscillator thatincludes the disclosed configuration of magnetically coupledmulti-inductors. By using the magnetically coupled inductors in amulti-phase oscillator, the multi-phase oscillator may have a reducedamount of jitter and a wide tuning range. Further, due to theoverlapping configuration of the inductors, the total amount of areaneeded to implement the multi-phase oscillator may be reduced. Inanother embodiment, the apparatus is a phase interpolator that combinesdifferent input signals by using the disclosed configuration of coupledinductive elements.

Reference will now be made in detail to several embodiments of thepresent disclosure, examples of which are illustrated in theaccompanying figures. It is noted that wherever practicable similar orlike reference numbers may be used in the figures and may indicatesimilar or like functionality. The figures depict embodiments of thepresent disclosure for purposes of illustration only. One skilled in theart will readily recognize from the following description thatalternative embodiments of the structures and methods illustrated hereinmay be employed without departing from the principles, or benefitstouted, of the disclosure described herein.

FIG. 1A illustrates a single stage of a magnetically-coupled oscillator108 in a loop of magnetically-coupled oscillators, according to anembodiment. The oscillator 102 includes an LC tank 104 for storingenergy and an energy-injection component 106 for injecting energy intothe LC tank 104. The LC 104 tank may include one or more capacitiveelements and one or more inductive elements. The LC tank 104 may beconfigured to generate one or more output signals 108 that oscillate ata particular frequency and at a particular phase relative to the phaseof other oscillators in the loop. The frequency of the outputoscillation signal 108 of the LC tank 104 depends on characteristics ofthe LC tank (e.g., the inductance and capacitance of the tank). Thephase of the output oscillation signal 108 generated by the LC tank 104will depend on the phase of the collective energy injected into the LCtank.

Because the LC tank 104 typically includes some parasitic resistancethat will reduce the energy of the tank and thereby dampen theoscillations of the LC tank 104 from an original energy supply, theenergy injection component 106 is used to replenish the loss of energydue to the resistance of the LC tank to maintain oscillation in the LCtank 104. Energy injection component 106 may be considered a negativeresistance element with respect to the parasitic resistance of the LCtank 104. The energy injection component 106 injects or suppliessupplemental energy (e.g., current) 105 (I_(N)) into the LC tank 104 tocompensate for the parasitic resistance of the LC tank's 104 elements.The energy injection component 106 may, for example, be implemented withone or more pairs of cross coupled transistors that are connected to anenergy source (not shown in FIG. 1A).

To set the oscillation of the LC tank 104 to a desired phase relative toother oscillators, two or more magnetic fluxes 110A, 110B are generated(also shown as Φ_(C(N−1)) and Φ_(C(N+1))) to inject energy into the LCtank 104. The magnetic fluxes are generated as a result of magneticcoupling between the inductive elements of the LC tank 104 and inductiveelements of LC tanks in other oscillators in the loop (not shown in FIG.1A). For example, magnetic coupling between the inductors of the LC tank104 and inductors of another oscillator can be achieved by overlappingthe coils of different inductors to form a type of transformer. When acurrent passes through an inductor of the other oscillator, it generatesa magnetic flux through the inductor of the LC tank 104, which in turninduces a current in the LC tank 140. The additional oscillators may beconfigured with the same circuit elements as discussed with respect tothe oscillator 102 of FIG. 1.

Generally, the magnetic fluxes 110 and the negative resistance signal105 will operate at a common frequency. However, the magnetic fluxes110A, 110B have phases that are different or offset from each other anddifferent or offset from the phase of the negative resistance signal105. Moreover, the fluxes may be generated such that the degree of eachof the phases of the fluxes cancel so that a total flux resulting fromtheir combination will have a phase approximately equal to that of thephase of the negative resistance signal 105. In this sense, the combinedphases of the fluxes 110A and 110B are balanced with respect to thephase of the internal energy of the oscillator.

Referring now to FIG. 1B, illustrated is a phase diagram ofcurrents/magnetic flux at one of the output nodes of the oscillator ofFIG. 1A, according to an embodiment. As illustrated, a first magneticflux Φ_(C(N−1)) has a first phase of +Θ. A second magnetic fluxΦ_(C(N+1)) has a second phase of −Θ. The phase of the first magneticflux Φ_(C(N−1)) lags the phase of the negative resistance signal I_(N)and the phase of the second magnetic flux Φ_(C(N+1)) leads the phase ofthe negative resistance signal. Thus, when the two fluxes are combined,the resultant flux (shown as Φ_(C(N−1))+Φ_(C(N+1))) has a phase that issubstantially equal to the phase of the negative resistance signalI_(N). When the fluxes are combined with the negative resistance signalI_(N) for injecting the joint energy into the tank 104, they willgenerally be in phase with the internal energy of the LC tank 104.

FIG. 2 illustrates an example circuit diagram for the oscillator 102 ofFIG. 1, according to an embodiment. Inductor 220 and capacitor 222 forman LC tank, such as LC tank 104 of FIG. 1. The inductor 220 ismagnetically coupled to inductors of at least two other oscillators (notshown in FIG. 2). A magnetic flux Φ_(C(N−1)) generated in the inductor220 by the magnetic coupling injects energy into the LC tank. Anothermagnetic flux Φ_(C(N+1)) generated in the inductor 220 by the magneticcoupling also injects energy into the LC tank. Two cross coupledtransistor pairs 224 and 226 form an energy injection component, such asenergy injection component 106 of FIG. 1, to inject a negativeresistance signal I_(N) into the LC tank. Complementary versions of theoutput oscillation signal from the tank may be taken at points V_((N)−)or V_((N)+).

In other embodiments, other configurations of the LC tank and energyinjecting component are possible. For example, the inductor 220 may be acenter-tapped inductor that is connected to a supply voltage, and theenergy injecting component may only include a single pair 224 of crosscoupled transistors without the second pair 226 of cross coupledtransistors.

FIG. 3 illustrates magnetic coupling between several oscillators,according to an embodiment. Shown is an oscillator 302(N) that ismagnetically coupled to additional oscillators 302(N+1) and 302(N−1).The components of each oscillator may be configured similarly andinclude components similar to those found in FIG. 2. As indicated by thedashed lines in FIG. 3, the inductor of oscillator 302(N) ismagnetically coupled to both the inductor of oscillator 302(N+1) and theinductor of oscillator 302(N−1). The inductor of oscillator 302(N)generates a magnetic flux Φ_(C1(N)) in the inductor of oscillator302(N+1) and a magnetic flux Φ_(C2(N)) in the inductor of oscillator302(N−1). The inductor of oscillator 302(N+1) generates a magnetic fluxΦ_(C2(N+1)) in the inductor of oscillator 302(N). The inductor ofoscillator 302(N−1) generates a magnetic flux Φ_(C1(N−1)) in theinductor of oscillator 302(N). Oscillators 302(N−1) and 302(N+1) may befurther magnetically coupled to other oscillators (not shown) in thismanner.

A large number of oscillators may be magnetically coupled to each otherin a loop in this manner. By coupling multiple oscillators in this way,multiphase output oscillation signals may be produced such that each Noscillator generates an output oscillation with a constant phasedifference with a next N+1 oscillator by a degree that is a function ofthe number of oscillators coupled together. Advantageously, magneticallycoupled multi-phase oscillators may have a reduced amount of jitter anda wider tuning range when compared to actively coupled multi-phaseoscillators. For example, multi-phase oscillators that are activelycoupled together through transistors have a high amount of noise due tothe active devices, which adds to the jitter of the output oscillationsignals. Additionally, the extra routing needed for the active couplingintroduces a parasitic capacitance that decreases the tuning range ofthe oscillator. Thus, by obviating the need for active coupling, thejitter performance and tuning range of the multi-phase oscillator may beimproved.

FIG. 4 illustrates a multi-phase oscillator, in accordance with anembodiment. The arrangement includes four oscillators 402-1, 402-2,402-3, and 404-4 for producing multi-phase clock signals. Eachoscillator may be constructed as described in FIG. 1 and FIG. 2. Eachoscillator is magnetically coupled to its neighboring oscillator to forma ring of oscillators. Thus, oscillator 402-1 is magnetically coupled tooscillator 402-2 and 402-4. Oscillator 402-2 is magnetically coupled tooscillator 402-1 and 402-3. Oscillator 402-3 is magnetically coupled tooscillator 402-2 and 402-4. Oscillator 402-4 is magnetically coupled tooscillator 402-1 and 402-3.

Each oscillator 402 is shown with a phase diagram (e.g., 412) thatrepresents the energy injected into the oscillator 402 and the operatingphase of the oscillator relative to other oscillators in the loop, whichwas previously explained in conjunction with FIG. 1B. The magneticcoupling between the oscillators 402 is labeled with arrows (e.g. 410,411) that indicate the phase of the energy injected into an oscillatorvia magnetic coupling. The phase of an oscillator typically follows theaggregate phase of the energy that is injected into the oscillator. Forexample, oscillator 402-1 injects energy 410 via magnetic coupling intooscillator 402-2 that has the same phase as the oscillations 424 ofoscillator 402-1. Oscillator 402-3 injects energy 411 into oscillator402-2 via magnetic coupling that has the same phase as the internalenergy of oscillator 402-3. The aggregate phase of the energy 410 and411 injected via magnetic coupling into oscillator 402-2 sets the phase412 of oscillator 402-2. Thus, the phase of each oscillator iseffectively set according to the phases of the adjacent oscillators inthe ring of oscillators. The same principles apply to each of theoscillators 402 of FIG. 4.

Generally speaking, the energy injected into an oscillator 402 viamagnetic coupling is in phase with the oscillator providing the energy.However, with respect to the magnetic coupling between oscillators 402-1and 402-4, the coupling is configured to create a 180 degree phaseinversion around the loop of oscillators. Thus, in the case of a loopconfiguration of N oscillators, the magnetic coupling between the 1^(st)oscillator and the Nth oscillator will be inverted from the coupling ofthe other oscillators. This permits a full rotation of the phases of theoutput oscillation signals between existing oscillators. For example,the energy 421 that is injected into oscillator 402-1 by oscillator402-4 via magnetic coupling is reversed from the phase 423 of theoscillator 402-4 providing the energy. Similarly, the energy 422 that isinjected into oscillator 402-4 by oscillator 402-1 via magnetic couplingis reversed from the phase 424 of the oscillator 402-1 providing theenergy. In one embodiment, the in-phase and out-of phase magneticcoupling between the oscillators in FIG. 4 may be accomplished with theinductor configuration shown in FIGS. 6A, 6B, and 6C.

Each oscillator generates two output oscillation signals that aresubstantially opposite in phase to each other. Oscillator 402-1generates output oscillation signals +/−V₁. Oscillator 402-2 generatesoutput oscillation signals +/−V₂. Oscillator 402-3 generates outputoscillation signals +/−V₃. Oscillator 402-4 generates output oscillationsignals +/−V₄.

FIG. 5 illustrates the phase relationship of the output oscillationsignals from the multi-phase oscillator of FIG. 4. Due to the chosennumber of oscillators and their coupling with each other, the outputoscillation signals from each oscillator (shown as + or −Vn) are eachforty five degrees out of phase with the signals of the immediatelypreceding oscillator. Output signal +V₁ is 45 degrees out of phase withoutput signal +V₂. Output signal +V₂ is 45 degrees out of phase withoutput signal +V₃. Output signal +V₃ is 45 degrees out of phase withoutput signal +V₄. Output signal +V₄ is 45 degrees out of phase withoutput signal −V₁. Output signal −V₁ is 45 degrees out of phase withoutput signal −V₂. Output signal −V₂ is 45 degrees out of phase withoutput signal −V₃. Output signal −V₃ is 45 degrees out of phase withoutput signal −V₄. Thus, this arrangement of oscillators with thisproduction of output oscillation signal may be used to generatequadrature clock signals by taking the outputs of every other oscillator402. Generally speaking, if there are N number of oscillators, the phasedifference from the output of one oscillator to the output of the nextoscillator is 180/N.

FIG. 6A illustrates a structure of magnetically coupled inductors forthe oscillators of FIG. 4, according to one embodiment. As shown, thetopology includes four different inductors: L1, L2, L3 and L4. In oneembodiment, the inductors are manufactured in one or more metal layersin a semiconductor process. The solid lines represent metal in one metallayer (e.g., M1 layer), and the diagonally hatched lines represent metalin a different metal layer (e.g., M2 layer). The different metal layersmay be connected by vias (not shown). As shown, both L1 and L3 are madefrom metal in two different metal layers. Both L2 and L4 are made frommetal in a single metal layer. In other embodiments, the inductors maypatterned on a printed circuit board or be discrete components that haveoverlapping coils.

In one embodiment, L1 represents the inductor in oscillator 402-1, L2represents the inductor in oscillator 402-2, L3 represents the inductorin oscillator 402-3, and L4 represents the inductor in oscillator 402-4.For purposes of showing the magnetic coupling among inductors withclarity, other components of the oscillators, such as capacitors andcross-coupled transistors, are omitted from FIG. 6A. L2 and L4 are eachcomprised of one large inductive coil. L1 and L3 are each comprised ofseveral coils.

The coils of the various inductors overlap to create a loop ofinductors. Each inductor overlaps with and is magnetically coupled toits adjacent inductors—both the next inductor in the loop and theprevious inductor in the loop. In region 690, a portion of inductor L1overlaps with a portion of inductor L2 to create magnetic couplingbetween inductor L1 and inductor L2. In region 691, another portion ofinductor L2 overlaps with a portion of inductor L3 to create magneticcoupling between inductor L2 and inductor L3. In region 693, anotherportion of inductor L3 overlaps with a portion of inductor L4 to createmagnetic coupling between inductor L3 and inductor L4. In region 692,another portion of inductor L4 overlaps with another portion of inductorL1 to create magnetic coupling between inductor L4 and inductor L1. Themagnetic coupling between the inductors allows the current passingthrough one inductor to generate a magnetic flux that induces a currentthrough another inductor. Additionally, by physically overlapping theinductors in this manner, the total amount of area that is occupied bythe multi-phase oscillator is also reduced. For example, if theinductors were non-overlapping, they would occupy approximately twice asmuch area on an integrated circuit.

The coils of inductor L1 are not all oriented in the same direction.Some of the coils 695 of inductor L1 are forward coils that carrycurrent in one direction. Some of the coils 696 of inductor L1 arereverse coils that are inverted from the forward coils 695 and carry thesame current in the opposite circular direction from the forward coils.As a result, the magnetic coupling between inductors L4 and L1 isreversed from the magnetic coupling between inductors L4 and L3 tocreate a 180 degree phase shift around the ring of oscillators. Themagnetic coupling is explained in greater detail by reference to FIG.6B-6E.

In some embodiments, the inductors may have a fewer or greater number ofcoils than is shown in FIG. 6A. In other embodiments, the configurationof inductors may be directly opposite from that shown in FIG. 6A. Forexample, in FIG. 6A, only inductor L1 has forward and reverse coils. Thesame 180 degree phase shift can also be implemented by an inductivestructure where L1 is composed of a single large coil and the remaininginductors (e.g., L2, L3, L4) have forward and reverse coils.

FIG. 6B illustrates the magnetic flux generated by inductor L1,according to an embodiment. Inductor L1 can be divided into forwardcoils 695 and reverse coils 696 that carry the same current 631 inopposite circular directions. When a current 631 flows through inductorL1, the current 631 flows in a clockwise direction 635 through theforward coils 695 and generates a magnetic flux 632 in one direction(i.e., into the page) for inductor pair L1-L2. The same current 631flows in a counter-clockwise direction 636 through the reverse coils 696and generates a magnetic flux 633 that is oriented in a substantiallyopposite direction (i.e., out of the page) for inductor pair L1-L4.

The layout of inductor L1 results in normal coupling between inductorsL1 and L2 and reverse coupling between inductors L1 and L4. The reversecoupling between inductors L1 and L4 creates the 180 degree phase shiftaround the ring of oscillators that is depicted in FIG. 4. As thecurrent 631 may be an AC current that switches directions over time, theflux directions shown in FIG. 6B represent the directions of the flux ata given instant in time when the current 631 is flowing in the indicateddirection.

FIG. 6C illustrates the magnetic flux generated by inductor L2,according to an embodiment. For inductor L2, the flux lines generated inadjacent inductors L1 and L3 by a current 601 flowing through inductorL2 are oriented in a common direction. For example, when current 601flows through inductor L2, it generates a magnetic flux 602 through aportion of inductor L1 and a magnetic flux 603 through a portion ofinductor L3 at a given instance in time. Both magnetic fluxes 602 and603 are oriented in a common direction (i.e., into the page). Fluxes 602and 603 may further generate currents in L3 and L2 that induce into thepage flux in the L3-L4 pair and out of the page flux in the L1-L4 pair(not shown).

FIG. 6D illustrates the magnetic flux generated by inductor L4,according to an embodiment. For inductor L4, the flux lines generated inadjacent inductors L1 and L3 by a current 601 flowing through inductorL4 are oriented in a common direction. For example, when a current 611is flowing through inductor L4, it generates a magnetic flux 612 througha portion of inductor L1 and a magnetic flux 613 through a portion ofinductor L3. Both magnetic fluxes are oriented in a common direction(i.e., into the page).

FIG. 6E illustrates the magnetic flux generated by inductor L3,according to an embodiment. For inductor L3, the flux lines generated inadjacent inductors L2 and L4 by a current 621 flowing through theinductor L3 at some given instant in time are oriented in a commondirection. For example, when a current 621 flows through inductor L3, itgenerates a magnetic flux 622 through a portion of inductor L2 and amagnetic flux 623 through a portion of inductor L4 that are oriented ina common direction (i.e., into the page).

FIG. 7 illustrates the structure of inductors for a multi-phaseoscillator that has only three oscillators, according to anotherembodiment. As shown, the structure includes three inductors L1, L2, andL3, each of which corresponds to one of the three oscillators of themulti-phase oscillator. Inductors L1 and L2 are partially overlappingand magnetically coupled to each other. Inductors L2 and L3 arepartially overlapping and magnetically coupled to each other. InductorsL1 and L3 are also partially overlapping and magnetically coupled toeach other.

Inductor L1 is configured with two coils that carry current in the samecircular directions. Thus, when a current (not shown) passes throughinductor L1, it generates a magnetic flux through inductor L2 and amagnetic flux through L3 that are oriented in the same direction.Inductor L2 is configured with two coils that carry current in the samecircular directions. Thus, when a current (not shown) passes throughinductor L2, it generates a magnetic flux through inductor L1 and amagnetic flux through L3 that are oriented in a common direction (notshown).

Inductor L3 is configured with a forward coil and a reverse coil thatcarry current in opposite circular directions. Thus, when a current 701passes through inductor L3, it generates a magnetic flux 703 throughinductor L1 that is oriented in one direction (i.e., into the page) anda magnetic flux 702 through inductor L3 that is oriented in asubstantially opposite direction. (i.e., out of the page). Theconfiguration of inductors in FIG. 7 results in normal magnetic couplingbetween inductors L2-L3 and inductors L1-L2, but reverse magneticcoupling between inductors L1-L3 to cause a 180 degree phase shift inthe coupling around the loop of oscillators.

Additionally, unlike the multi-phase oscillator in FIG. 4, a multi-phaseoscillator that incorporates the magnetically coupled inductors in FIG.7 only has a total of three oscillators. The multi-phase oscillatorrepresented by FIG. 7 thus generates oscillation output signals that are60 degrees out of phase with each other as opposed to 45 degrees out ofphase with each other.

FIG. 8 illustrates a phase interpolator/mixer that uses the inductivestructure of FIG. 6A, according to yet another embodiment. The phaseinterpolator includes four inductors, L1, L2, L3 and L4 with overlappingcoils. A gain circuit 805 receives a differential input signal Q,adjusts the amplitude of the signal by a factor of β, and applies theresulting signal to inductor L1. A gain circuit 807 receives adifferential input signal I, adjusts the amplitude of the signal by afactor of a, and applies the resulting signal to inductor L3. In oneembodiment, I and Q are quadrature signals that are 90 degrees out ofphase with each other.

Due to the magnetic coupling between inductors L1, L2, and L3, an outputsignal αI+βQ 811 is generated at the port of inductor L2. Output signal811 represents the sum of the amplitude adjusted input signals I and Q.Due to the magnetic coupling between L1, L3, and L4, another outputsignal αI−βQ 813 is generated at the port of inductor L4. Because of thereverse coupling between inductors L1 and L4, output signal 813represents the difference between the amplitude adjusted input signals Iand Q.

FIG. 9 illustrates an apparatus 900 with four circuit stages 905,according to an embodiment. The four circuit stages 905 are coupledtogether as a loop or ring of circuit stages 905. Each circuit stage 905includes an inductive element (not shown) that is magnetically coupledto the inductive element of its adjacent circuit stages 905 to formpairs of circuit stages. The magnetic coupling is reversed betweencircuit stage 905-1 and 905-4 to create a 180 degree phase inversionaround the loop of circuit stages. The structure of the inductiveelements and the coupling between the inductive elements may be similarto that shown in FIG. 6A. In other embodiments, there may be a differentnumber of circuit stages 905, so long as there are three or more circuitstages 905 in the loop. Each circuit stage 905 also has a port 910 forreceiving input signals or outputting output signals, depending on theembodiment.

In one embodiment, the apparatus 900 is a multi-phase oscillator. Eachof the circuit stages 905 of the multi-phase oscillator may be similarto the oscillator stage 102 of FIG. 1A. Each port 910 may be an outputport for outputting multi-phase signals. Each signal has substantiallythe same frequency as the other output signals but oscillates atdifferent phases relative to the other signals as shown in FIG. 5.

In one embodiment, the apparatus 900 is a phase interpolator. In thisembodiment, some of the circuit stages 905 may be input stages. Forexample, referring to both FIG. 8 and FIG. 9, circuit stage 905-1 may bean input stage that includes amplifier 805 and inductor L1. Circuitstage 905-3 may be an input stage that includes amplifier 807 andinductor L3. Some of the circuit stages may be output stages. Forexample, circuit stage 905-2 may be an output stage that includesinductor L2 and circuit stage 905-4 may be an output stage that includesinductor L4. Port 910-1 and 910-3 may be input ports that receive inputsignals, and ports 910-2 and 910-4 may be output ports for outputtingoutput signals.

In this disclosure, a multi-phase oscillator and a phase interpolatorhave been provided as two examples of an apparatus that use thedisclosed configuration of magnetically coupled inductors. Otherapparatuses that use the disclosed configuration of magnetically coupledinductors may include, for example, a feed network for a phase arrayantenna. Some of these embodiments may be implemented, for example, aspart of an integrated circuit device.

Upon reading this disclosure, those of skill in the art will appreciatestill additional alternative designs for an apparatus that includesmagnetically coupled inductors. Thus, while particular embodiments andapplications of the present disclosure have been illustrated anddescribed, it is to be understood that the disclosure is not limited tothe precise construction and components disclosed herein. Variousmodifications, changes and variations which will be apparent to thoseskilled in the art may be made in the arrangement, operation and detailsof the method and apparatus of the present disclosure herein withoutdeparting from the spirit and scope of the disclosure as defined in theappended claims.

1. An apparatus, comprising: N circuit stages coupled in a loop, N>2,each of the N circuit stages having an inductive element that overlapswith inductive elements from two adjacent circuit stages in the loop,the overlapping inductive elements forming N pairs of inductivelycoupled elements including a first pair and a second pair of inductivelycoupled elements, wherein a magnetic flux induced in a first pair ofinductively coupled elements is oriented in a first direction at a giventime, and wherein a magnetic flux induced in a second pair ofinductively coupled elements is oriented in a second direction,substantially opposite to the first direction at the given time.
 2. Theapparatus of claim 1, wherein magnetic fluxes induced in remaining pairsof the N pairs of inductively coupled elements are oriented in the firstdirection.
 3. The apparatus of claim 1, wherein the first and secondpairs of inductive elements share a common inductive element, the commoninductive element inducing the magnetic fluxes in the first and secondpairs of inductively coupled elements.
 4. The apparatus of claim 1,further comprising a plurality of output ports, each output portassociated with a corresponding one of the N circuit stages, whereineach output port outputs at least one output signal having substantiallythe same frequency and each output signal has a phase difference from atleast one output signal of an adjacent circuit stage.
 5. The apparatusof claim 4, wherein the phase difference is substantially equal to 180degrees divided by N (180°/N).
 6. The apparatus of claim 4, wherein atleast two of the output signals have a quadrature phase relationship. 7.The apparatus of claim 1, wherein the inductive element for each circuitstage forms part of an LC tank for the circuit stage, and each of the Ncircuit stages further comprises an energy injecting component forinjecting energy into the LC tank.
 8. The apparatus of claim 1, furthercomprising: a first port associated with a first circuit stage andreceiving a first input signal, wherein the magnetic fluxes are inducedthe first and second pairs of inductively coupled elements based on theinput signal; and a second port associated with a second circuit stageand receiving a second input signal, wherein a third circuit stagegenerates a first output signal indicative of a sum of the inputsignals, wherein a fourth circuit stage generates a second output signalindicative of a difference between the input signals.
 9. The apparatusof claim 8, wherein: the first circuit stage includes a first amplifierthat amplifies the first input signal; the second circuit stage includesa second amplifier that amplifies the second input signal; wherein thefirst output signal is indicative of a sum of the amplified inputsignals; and wherein the second output signal is indicative of adifference between the amplified input signals.
 10. The apparatus ofclaim 1, wherein the apparatus comprises four circuit stages.
 11. Theapparatus of claim 1, wherein the apparatus is an integrated circuit.12. The apparatus of claim 1, wherein the inductive elements are formedin one or more metal layers on a substrate.
 13. The apparatus of claim1, wherein the inductive elements are formed in one or more metal layersof a printed circuit board. 14-18. (canceled)
 19. A multi-phaseoscillator comprising: N oscillator stages coupled as a loop ofoscillator stages, N>2, each oscillator stage comprising a LC tank andan energy injection component for injecting energy into the LC tank,wherein each LC tank comprises an inductive element that overlaps withinductive elements of LC tanks from two adjacent oscillator stages inthe loop; and a plurality of output ports, each output port associatedwith a corresponding one of the N oscillator stages, wherein each outputport outputs at least one output signal having substantially the samefrequency and each output signal has a phase difference from at leastone output signal of an adjacent oscillator stage.
 20. The oscillator ofclaim 19, wherein each LC tank oscillates at substantially the samefrequency and each LC tank has a phase difference from the LC tank of anadjacent oscillator stage.
 21. (canceled)
 22. The oscillator of claim19, wherein the phase difference is substantially equal to 180 degreesdivided by N (180°/N).
 23. The oscillator of claim 19, wherein at leasttwo of the output signals have a quadrature phase relationship.
 24. Aphase interpolator, comprising: N circuit stages coupled as a loop ofcircuit stages, each circuit stage comprising an inductive element thatoverlaps with inductive elements of two adjacent oscillator stages inthe loop, the N circuit stages including a first, second, third, andfourth circuit stages; a first port associated with a first circuitstage for receiving a first input signal; a second port associated witha second circuit stage for receiving a second input signal; wherein athird circuit stage generates an first output signal indicative of a sumof the input signals; and wherein fourth circuit stage generates asecond output signal indicative of a difference between the inputsignals.
 25. The phase interpolator of claim 24, wherein: the firstcircuit stage comprises a first amplifier that amplifies the first inputsignal; and the second circuit stage comprises a second amplifier thatamplifies the second input signal; wherein the first output signal isindicative of a sum of the amplified input signals, and wherein thesecond output signal is indicative of a difference between the amplifiedinput signals.
 26. The phase interpolator of claim 24, wherein theinductive elements are formed in one or more metal layers on a substrateor formed in one or more metal layers of a printed circuit board.